theorem Th5:
  for k,l holds l is CQC-variable_list of k,Al2
proof
  let k,l;
  rng l c= bound_QC-variables(Al) &
     bound_QC-variables(Al) c= bound_QC-variables(Al2) by Th4;
  then rng l c= bound_QC-variables(Al2);
  hence thesis by FINSEQ_1:def 4, XBOOLE_1:1;
end;
